It’s interesting that we had reverse experiences regarding the recent FF titles. I think for me, it was because I played them very close to each other, and I probably would have been fed up by halfway through whichever one I played second. My gaming buddy mostly really liked Rebirth.
But they both had a slightly different version of this same issue, and my tolerance was pretty low by the time I got to Rebirth.
I have tried many times to do exactly what you said, and I still am not getting the option to add a custom search engine.
Any advice you have is appreciated.